Cryptography was used extensively during World War II because of the importance of radio communication and the ease ofradio interception. The nations involved fielded a plethora ofcode andcipher systems, many of the latter usingrotor machines. As a result, the theoretical and practical aspects ofcryptanalysis, orcodebreaking, were much advanced.
Possibly the most important codebreaking event ofthe war was the successful decryption by the Allies of the German"Enigma" Cipher. The firstbreak into Enigma was accomplished byPolish Cipher Bureau around 1932; the techniques and insights used were passed to the French and British Allies just before the outbreak of the war in 1939. They were substantially improved by British efforts atBletchley Park during the war. Decryption of theEnigma Cipher allowed the Allies to read important parts of German radio traffic on important networks and was an invaluable source ofmilitary intelligence throughout the war. Intelligence from this source and other high level sources, such asCryptanalysis of the Lorenz cipher, was eventually calledUltra.[1][2][3]
A similar break into the most secure Japanese diplomatic cipher, designatedPurple by the US Army Signals Intelligence Service, started before the US entered the war. Product from this source was calledMagic.
On the other side,German code breaking in World War II achieved some notable successes cracking British naval and other ciphers.
